Study Of C2 Alcohol Oxidation Reactions On Pd Electrocatalysts: The Structure Effect And The Infrared Spectroscopy Approach

Both direct and indirect ways can be generally used for converting hydrogen energy stored in C2 alcohol molecules into electricity: The former is realized by means of direct alcohol fuel cells,which are promising for powering portable devices.The latter is achieved by sacrificing the C2 alcohol molecules in the anode of an electrolytic cell to produce H2 in the cathode for feeding the H2-O2 fuel cells.In both cases,the electro-oxidation of C2 alcohols is essential.The critical step is the selective activation of C2 alcohol and the fast oxidation of intermediates on the catalysts.At present,noble metal Pt is the most widely used anode catalyst in the C2 alcohol fuel cell.Due to the rarity and high cost of Pt,Pd-based catalysts have been investigated as alternative promising catalytic materials for C2 alcohol oxidation in alkaline media given that they may outperform traditional Pt-based ones in term of electrocatalytic activities.Therefore,it is of great significance to study Pd based catalysts in the application for the alkaline alcohols fuel cells.In this work,in order to establish the correlation between the surface structure and catalytic performance,we synthesized three low index Pd nanocrystals and further investigated the C2 elcetro-oxidation on these nanocrystals to clarify crystal orientation effect.Secondly,Bi atoms were modified on the Pd cube to enhance the property of C2 alcohol oxidation.In addition,the superior duability mechanism for catalyzing ethanol oxidation on Pd/Ni(OH)2/r GO(ultrathin Ni(OH)2 combine with r GO as composite support)was also verified by SEIRAS.The main contents and results are as follows:(1)C2 alcohol oxidation on three low index Pd nanocrystals in alkaline media.Electrocatalytic reaction is occurred on the interfacial surface of the catalyst.C2 alcohols electrocatalytic reactions on Pd surfaces are known to be facetsensitive.Pd cubes,Pd Octs and Pd RDs are closed by three basal planes {100},{111} and {110} respectively,and are of fundamental interest since they may be combined to constitute structurally higher index planes of single crystals.These three types of nanocrystals were obtained via wet chemistry one-pot synthesis,and then the clean surface was obtained by effectively utilizing the COadsorption displacement tactics.A systematic investigation into the electrocatalytic activities of these model Pd nanocatalysts for ethanol and ethylene glycol oxidation in alkaline media have been taken out through CV and i-t test.The experimental results combined with DFT calculation turned out that OHads and COads play an important role during C2 alcohol oxidation.The peak current densities of C2 alcohols oxidation on Pd Cubes is higher than that of Pd Oct and RD,while the onset potential of C2 alcohols oxidation on Pd RD is the lowest.(2)C2 alcohol oxidation on Bi-modified Pd nanocubes.Surface modification is an effective way to enhace the catalytic performance.The modification of Bi on Pd not only can transfer electrons from Bi to Pd changing the d-band centre of Pd,but also interrupt the continuous Pd sites on the surface of the catalyst changing the way of the adsorbed reaction species and the reaction path way on it.Bi atom was modified on the highest active Pd nanocubic surface via the potential cycling approach by limiting the scan potential and Bi-modified Pd was applied for C2 alcohols oxidation in alkaline media.The modification of Bi can significantly increase the electro-oxidation activity of C2 alcohol in alkaline media with an optimal Bi coverage.(3)ATR-IR spectroscopic characterization of adsorbed CO species.CO is an essential intermediate species in the electrooxidation of methanol and ethanol,it is of great importance to clarify the role of CO for designing and developping highly efficient catalysts.This chapter is mainly composed of two parts: Firstly,Pd nanoparticles loaded on Ni(OH)2/r GO as catalyst has been synthesized based on the understanding of the mechanism of the ethanol electrooxidation on the Pd electrode in alkaline media.Ultrathin Ni(OH)2 support material promotes CO desorption to release the active site,which was further confirmed by infrared spectroscopy measurement.Secondly,the catalytic performance of methanol oxidations on the Pt Ru catalyst can be enhanced by loading on an excellent conductive Ta C-C support material in acid media.The promoting effect of Ta C-C support material in CO desorption and releasing the active site has been verified by infrared spectroscopy study.